Process for preparing vincamine and its stereoisomers

ABSTRACT

Vincamine and/or its stereoisomers, a known drug, is made from vincaminol and/or its stereoisomers by successive conversion of the latter into apovincaldehyde, apovincamine, and 16methoxycarbonyl-eburnane, followed by conversion of the last into vincamine either directly by introduction of a 16-hydroxyl group or by hydrolysis, introduction of a 16-hydroxyl group, and reesterification.

United States Patent [1 1 Najer et al.

[ PROCESS FOR PREPARING VINCAMINE AND ITS STEREOISOMERS [75] inventors: Henry Najer; Yves Robert Alain Pascal, both of Paris, France [73] Assignee: Synthelabo, Paris. France [22] Filed: Dec. 12, 1973 [2|] Appl. No.: 423,901

UNITED STATES PATENTS 3,830,823 8/l974 Castaigne 26U/293.53

4 1 Dec.9, 1975 Primary ExaminerG. Thomas Todd Attorney, Agem, 0r FirmArmstrong, Nikaido &

Wegner ABSTRACT Vincumine and/or its stereoisomers, a known drug, is made from vincaminol and/or its stereoisomers by successive conversion of the latter into apovincaldehyde, apovincamine, and l6-methoxycarbonyl-eburnane, followed by conversion of the last into vincamine either directly by introduction of a l6-hydroxyl group or by hydrolysis. introduction of a l-hydroxyl group, and re-esteriflcation.

11 Claims, No Drawings PROCESS FOR PREPARING VINCAMINE AND ITS STEREOISOMERS The present invention provides a process for preparing vincamine and its stereoisomers from vincaminol, which is a known compound, the synthesis of which from indole has been described by Castedo, Harley- Masar and Leeney (Chem. Comms. 1968, 1186).

The process of the invention comprises converting vincaminol and/or its stereoisomers into apovincaldehyde and/or its stereoisomers, converting the latter into apovincamine and/or its stereoisomers, hydrogenating STEP l Vincaminol STEP II Apovin caldehyde apovincamine and/or its stereoisomers to give a mixture of lfi-methoxycarbonyl-eburnane stereoisomers, and either (A) converting the latter into a carbanion and introducing a hydroxyl radical at position 16 of this carbanion, to give vincamine, l6-epivincamine and/or their stereoisomers, or (B) saponifying the l6-rnethoxycarbonyl-ebumane stereoisomers to give lfi-carboxyebumanes, converting the latter into a carbanion, introducing a hydroxyl radical at position 16 of this anion, and esterifying the product to give vincamine, l6- epivincamine, and/or their stereoisomers.

The process of the invention may be represented by the following reaction scheme:

Apov in ca 1 dehyde New compound Carbanion Vincamine epivincamine or their stereoisomers In the variant of the process lfi-methoxycarbonyleburnanes are saponified to l6-carboxy-eburnanes before the conversion to the carbanion and the attachment of the OH radical at position 16. The vincaminic and epivincaminic acids obtained are then esterified. This variant (step IV bis) may be represented as follows:

STEP IV BIS tures (100 to +100C) depending on the reagents used, in an aprotic solvent such as anhydrous tetrahydrofuran or hexamethylphosphorotriamide or a mixture of the two, by the action of a strong organic base such as triphenylmethyl sodium, or an alkali metal amide, for example lithium diisopropylamide or lithium cyclohexylisopropylamide.

HO- OC carbanion or their stereoi somers vincaminic acid epivincaminic acid or their stereoisorners Vincamine alone may be obtained by adopting one of the following procedures:

I. The mixture of vincamine and epivincamine is treated under hot conditions with potassium hydroxide in an alcohol, for example methanol; this causes saponification with epimerisation, so that pure vincaminic acid is obtain ed The latter can then be esterified to give vincamine.

II. In the preceding stage, the mixture of vincaminic and epivincaminic acids is epimerised by treatment with potassium hydroxide; pure vincaminic acid is then collected and esterified to give Vincamine.

When epimerisation is not carried out, the proportion of vincamine in the mixture of Vincamine and epivincamine is approximately 50%. If so desired, after separation, it is possible to recycle the epivincamine which is converted to apovincamine.

Step I is an oxidising dehydration preferably carried out with phosphorus pentoxide and dimethylsulphoxide, at a temperature from to 150C, in the presence or absence of a solvent and, advantageously, with addition of pyridine.

Step II, the conversion of an aldehyde to an ester, is preferably carried out by reacting the aldehyde with an alkali metal cyanide, dissolved in a hydroxyl-containing solvent such as an alcohol, followed by oxidation, in the presence of acetic acid, with, for example, manganese dioxide. This reaction is carried out at the laboratory temperature.

Step III, hydrogenation of apovincamine, has already been described in particular by Trojanek and colleagues (Tet. Letters, 1961, 702) and by Clauder and colleagues (ibid. 1962, 1147)v The first part of step IV (conversion to the carbanion) may be carried out over a wide range of tempera- The second part of this step is effected by the action of molecular oxygen, and can consist of simply bubbling air into the reaction mixture.

In step IV bis, the prior saponification of the ester to the acid takes place under conventional conditions, using an alkali metal hydroxide, under cold conditions, in an alcohol, followed by acidification. The conversion to the carbanion and the attachment of the OH radical at position 16 by reaction of a strong organic base and passage of oxygen, are similar to that described in step IV. However, the reaction is generally carried out at a temperature of 0 to +C.

The subsequent esterification of the acids obtained is well known; see especially Trojanek et al. and Clauder et a]. (10c. cit).

The conversion of epivincamine to apovincamine is carried out by the action of acetic anhydride or formic acid.

The following non-limiting Example illustrates the invention.

EXAMPLE STEP I: Apovincaldehyde 10 ml of anhydrous pyridine followed by 5g of phosphorus pentoxide, added gradually in small amounts, are added to a solution of 5g (0.015 mol) of vincaminol in 50 ml of dimethylsulphoxide. A sponteneous rise in temperature is observed. The mixture is then heated for 1 hour at 100C, a further 10 ml of dimethylsulphoxide, 5 ml of pyridine and 5g of phosphorus pentoxide are added, followed again, after 2 hours, by 10 ml of pyridine and 5g of phosphorus pentoxide. The reaction is completed by adding a further 5g of phosphorus pentoxide after 1 hour, and by heating the reaction mixture for 3 hours at 100C.

The mixture is left to cool, and excess potassium carbonate is added, followed by water, added dropwise. The mixture is extracted three times in succession with 50 ml of ether, the combined ether extracts arewashed twice in succession with a saturated solution of sodium chloride, dried over sodium sulphate and filtered, and the solvent is driven from the filtrate on a water bath in vacuo.

The oily residue is chromatographed on alumina, eluting with benzene. In the eluate, after evaporation of the solvent, 3.7g (yield 80%) of apovincaldehyde are collected in the form of an oil which, when redissolved in petroleum ether (35709C) and precipitated by means of benzene, is in the form of a yellow crystalline compound, solvated with 1 molecule of benzene, which melts at 94C.

Analysis: C H N O (M. W.=306): Calculated: C, 81.3; H, 7.34. Found: C. 81.37: H, 7.34. STEP [1: Apovincamine 500 mg (0.0016 mol) of apovincaldehyde are dissolved in ml of anhydrous methanol, and 820 mg (0.017 mol) of sodium cyanide and 300 mg (0.005 mol) of acetic acid are added, followed, after ten minutes, by 5.75g (0.066 mol) of active manganese dioxide freshly prepared by the method of Corey, Gilman and Granem (.l.Amer.Chem.Soc., 1968, 90, page 5615) and finely ground. 1

The mixture is left to stand overnight at ambient temperature. Excess sodium bicarbonate is added and the mixture is extracted three times in succession with ethyl acetate. The combined ethyl acetate extracts: are washed in succession with 0.1 N sodium hydroxide solution and a saturated solution of sodium chloride; they are dried over sodium sulphate and filtered; the solvent is evaporated from the filtrate and apovincamine is crystallised by triturating the residual oil in diethyl ether. The ether is evaporated and the residue is triturated in petroleum ether (3570C) and drained.

450 mg (yield 82%) of apovincamine, mp. 162C, are thus collected; it is identified by its mixed melting point and its infra-red and NMR spectra, compared with an authentic sample.

STEP lll: Desoxyvincamines 14.1 g (0.042 mol) of apovincamine are dissolved in 250 ml of ethyl acetate, 2g of 5% palladium on charcoal are added and the mixture is hydrogenated over the course of 2 hours at 70C under 100 atmospheres initial pressure. The mixture is allowed to cool, the catalyst is filtered off and washed with chloroform and the solvents are evaporated from the filtrate.

13g (yield 92%) of a mixture of desoxyvincamines, which melts at l25130C, are thus collected.

STEP IV: vincamine and l6-epivincamine 3.4g (0.01 mol) of the mixture of desoxyvincamines are added to a solution of lithium cyclohexylisopropylamide in tetrahydrofuran, prepared beforehand from 1.4g (0.01 mol) of cyclohexylisopropylamine and 5 ml of a 2.14 N solution of butyl-lithium in diethyl ether, cooled to 78C.

A stream of air is bubbled into this mixture, gradually allowing the temperature to return to that of the laboratory. After bubbling for 48 hours, a saturated solution of sodium bicarbonate is added. The mixture is extracted several times with methylene chloride, and the combined methylene chloride extracts are dried over sodium sulphate and filtered; the solvent is evaporated from the filtrate on a water bath in vacuo, the oily residue is triturated in diethyl ether and the precipitate consisting of a mixture of vincamine and l6-epivincamine is filtered off.

STEP lV BIS:

l. Desoxyvincaminic and l6-epidesoxyvincaminic acids A suspension of 4g (0.012 mol) of the mixture of desoxyvincamines in a solution of 5g of potassium hydroxide in 50 ml of methyl alcohol is left to stand overnight, with stirring. Water is added, the pH is adjusted to 6.5 by adding 0.1 N hydrochloric acid, and the product is filtered off, washed with water and dried in vacuo over phosphorus pentoxide.

3.5g (yield 91%) of a mixture of desoxyvincaminic and l6-epidesoxyvincaminic acids, which melts at a temperature above 250C, are thus collected.

Analysis: C H O N (M.W.=324): Calculated: C, 73.91% H. 7.44: N, 8.65. Found: %C, 73.57; H. 7.51; N, 8.59.

2. Vincaminic and l-epivincaminic acids A mixture of 1.25g (0.004 mol) of desoxyvincaminic and 16 epidesoxyvincaminic acids is added to a solu' tion in anhydrous tetrahydrofuran of lithium diisopropylamide prepared at the time of use from 0.8g (0.008 mol) of diisopropylamine and 4 ml of a 2.1 N solution of butyl-lithium (0.0085 mol) in diethyl ether. The mixture is left to stand at 0C for 30 minutes and is then heated at 509C for 1 hour. It is cooled in an ice bath and a stream of airis bubbled into it for 6 hours. 10 m1 of methanol and 10 mlof water are then added and the pH of the solution is adjusted to pH 7.5 by means of N hydrochloric acid. A precipitate consisting of a mixture of vincaminic and 16-epivincaminic acids is thus obtained and is filtered off and dried for 2 hours at C over phosphorus pentoxide and under a residual vacuum of 20 mm.

1 g (yield 76%) of this mixture, which melts at a temperature above 250C, is finally collected.

Analysis: C l-l O N, (M.W.=340): Calculated: C, 70.6; H, 7.10; N, 8.24: %O, l4. 15. Found: C, 70.4; H, 7.13, N, 8.30; O, 13.9.

3. Vincamine and 16-epivincamine A solution of diazomethane in diethyl ether is added to a suspension of lg (0.003 mol) of the mixture of vincaminic and 16-epivincaminic acids in methylene chloride, cooled to 0C. The mixture is left to stand at am bient temperature for 2 hours and is acidified with acetic acid; the solvents are driven ofi on a water bath in vacuo and the residue is extracted with methylene chloride; the latter extract is washed in succession with a 0.1 N solution of sodium hyroxide and then with water, is dried over sodium sulphate and filtered; the solvent is evaporated on a water bath in vacuo.

The residue of 0.96g(yield 92%) is chromatographed on 30g of alumina. By eluting first with benzene and then with chloroform, vincamine and 16 epivincamine are collected separately.

Epimerisation A mixture of 200 mg (0.0006 mol) of vincamine and 16-epivincamine in 25 ml of methyl alcohol containing 200 mg (0.0036 mol) of potassium hydroxide is heated under reflux for 5 hours. The solvent is driven off and water is added, followed by 0.1 N hydrochloric acid until the pH is 6.5.

180 mg (yield 94%) of vincaminic acid are thus collected and are converted to vincamine by reaction with diazo methane.

Conversion of epivincamine to apovincamine A solution of 3.54g (0.01 mol) of l6-epivincamine in 50 ml of formic acid is heated under reflux for 10 hours, under nitrogen. The formic acid is evaporated on a water bath in vacuo, the residue is dissolved in methylene chloride, and the latter solution is washed with a saturated solution of sodium bicarbonate and with water. The solution is dried over sodium sulphate and filtered, and the methylene chloride is evaporated from the filtrate. 2.7g (yield 80%) of apovincamine are thus collected.

We claim:

1. A process for the preparation of vincamine, epivincamine or stereoisomer thereof which comprises (1) treating vincaminol or stereoisomer thereof to oxidizing dehydration to yield apovincaldehyde or stereoisomer, thereof; (ll) esterifying said apovincaldehyde or stereoisomer thereof into apovincamine or stereoisomer, thereof; (lll) hydrogenating said apovincamine or stereoisomer thereof to yield a mixture of lo-methoxycarbonyleburnane stereoisomers, (IV)A treating said mixture with a base to yield the carbanion thereof and treating said carbanion with molecular oxygen whereby there is produced a lo-hydroxy derivative, or (IV)B saponifying the l-methoxycarbonyl-eburnane stereoisomers to yield l6-carboxy-eburnanes, treating said 16- carboxy-eburnanes with a strong base to yield a carbanion, treating said carbanion with molecular oxygen to yield said l6-hydroxy derivative; and esterifying said l6-hydroxy derivative to yield vincamine, l6-epivincamine stereoisomers thereof.

2. A process of claim I, wherein step lV(B) is used to produce a product containing only vincaminic acid and stereoisomers thereof.

3. A process of claim I in which the vincamine of epivincamine product is saponified with epimerisation to yield a pure vincaminic acid which is then esterified to yield vincamine or stereoisomer thereof.

4. A process of claim I, wherein unreacted starting materials and stereoisomer byproducts are recycled.

5. A process of claim 4, wherein lo-epivincamine or stereoisomer thereof is recycled by conversion to apovincamine.

6. A process of claim 1 wherein said oxidising dehydration is efi'ected with phosphorus pentoxide and dimethylsulphoxide.

7. A process of claim I wherein apovincaldehyde or stereoisomer thereof is converted to apovincamine or stereoisomer thereof by the action of an alkali metal cyanide and by oxidation with maganese dioxide.

8. A process of claim 1 wherein the formation of said carbanion is effected in a dipolar aprotic solvent, at a temperature from lO0 to +C., by the action of a strong organic base.

9. A process of claim 7 wherein the dipolar aprotic solvent is anhydrous tetrahydrofuran or hexamethylphosphorotriamide or mixture thereof.

10. A process of claim 8 wherein the strong organic base is triphenyl-methyl-sodium or an alkali metal amide.

11. A process of claim 10 wherein the alkali metal amide is lithium diisopropylamide or lithium cyclohexylisopropylamide. 

1. A PROCESS FOR THE PREPARATION OF VINCAMINE, EPIVINCAMINE OR STEREOSOMER THEREOF WHICH COMPRISES (I) TREATING VINCAMINOL OR STEREOSOMER THEREOF TO OXIDIZING DEHYDRATION TO YIELD APOVINCALDEHYDE OR STEREOISOMER, THEREOF; (II) ESTERIFYING SAID APOVINCALDEHYDE OR STEREOSOMER THEROF INTO APOVINCAMINE OR STEREOISOMER, THEREOF; (III) HYDROGENATING SAID APOVINCAMINE OR STEREOISOMER TIEREOF TO YIELD A MIXTURE OF S16-MIETHOXYCARBONYLBURNANE STEREOISOMERS, (IV) A TREATING SAID MIXTURE WITH A BASE TO YIELD THE CARBANION THEREOF AND TREATING SAID CARBANION WITH MOLECULAR OXYGEN WHEREBY THERE IS PRODUCED A 16-HYDROXY DERIVATIVE, OR (IV)B SAPONIFYING THE 16-METHOXYCARBONYL-EBURNANE STEREOISOMERS TO YIELD 16-CARBOXY-EBURNANES, TREATING SAID 16-CARBOXY-EBURNANES WITH A STRONG BASE TO YIELD A CARBONION, TREATING SAID CARBANION WITH MOLECULAR OXYGEN TO YIELD SAID 16-HYDROXY DERIVATIVE; AND ESTERIFYING SAID 16-HYDROXY DERIVATIVE TO YIELD VINCAMINE, 16-EPIVINCAMINE STEREOISOMERS THEREOF.
 2. A process of claim 1, wherein step IV(B) is used to produce a product containing only vincaminic acid and stereoisomers thereof.
 3. A process of claim 1 in which the vincamine of epivincamine product is saponified with epimerisation to yield a pure vincaminic acid which is then esterified to yield vincamine or stereoisomer thereof.
 4. A process of claim 1, wherein unreacted starting materials and stereoisomer byproducts are recycled.
 5. A process of claim 4, wherein 16-epivincamine or stereoisomer thereof is recycled by conversion to apovincamine.
 6. A Process of claim 1 wherein said oxidising dehydration is effected with phosphorus pentoxide and dimethylsulphoxide.
 7. A process of claim 1 wherein apovincaldehyde or stereoisomer thereof is converted to apovincamine or stereoisomer thereof by the action of an alkali metal cyanide and by oxidation with maganese dioxide.
 8. A process of claim 1 wherein the formation of said carbanion is effected in a dipolar aprotic solvent, at a temperature from -100* to +100*C., by the action of a strong organic base.
 9. A process of claim 7 wherein the dipolar aprotic solvent is anhydrous tetrahydrofuran or hexamethyl-phosphorotriamide or mixture thereof.
 10. A process of claim 8 wherein the strong organic base is triphenyl-methyl-sodium or an alkali metal amide.
 11. A process of claim 10 wherein the alkali metal amide is lithium diisopropylamide or lithium cyclohexylisopropylamide. 